Interaction between polyene antifungal drug and saturated phospholipid monolayer regulated by calcium ions at the air-water interface

Regulation of calcium ions on the interaction between amphotericin B and cholesterol-rich phospholipid monolayer in LE phase and LC phase

Amphotericin B, as a "gold standard", is used to treat invasive fungal infections. The AmB molecule can bind easily to cholesterol and damage cell membranes, so it produces the toxicity on cell membrane, which limits its clinical dose. However, the interaction between AmB and cholesterol-rich membrane is unclear now. The phase state of the membrane and the metal cation outside cell membrane may affect the interaction between AmB and the membrane. In this work, the effects of amphotericin B on the mean molecular area, elastic modulus and stability of mammalian cell membrane rich in cholesterol in the presence of Ca²⁺ ions were studied using DPPC/Chol mixed Langmuir monolayer as a model. The Langmuir-Blodgett method and AFM test were used to study the effects of this drug on the morphology and height of cholesterol-rich phospholipid membrane in the presence of Ca²⁺ ions. The influence of calcium ions on the mean molecular area and the limiting molecular area was similar in LE phase and in LC phase. The calcium ions made the monolayer more condensed. However, calcium ions can weaken the shortening effect of AmB on the relaxation time of the DPPC/Chol mixed monolayer in LE phase but enhance it in LC phase. Interestingly, calcium ions caused a LE-LC coexistence phase to occur in the DPPC/Chol/AmB mixed monolayers at 35mN/m, which was confirmed by atomic force microscopy. The results can help to understand the interaction between amphotericin B and cell membrane rich in cholesterol in the calcium ions environment.

Biological activity of pectic polysaccharides investigated through biomembrane models formed at the air-water interface

Pectin, a polysaccharide with potential bioactivity, was inserted in the aqueous subphase of monolayers of the selected lipids DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine), representing mammalian and bacterial membranes, respectively. Pectin condensed both monolayers but made the DPPC monolayer more fluid, while for DPPE, it made its monolayer more rigid, as detected with dynamic interfacial rheology. Complementary data using surface potential, infrared spectroscopy, and Brewster angle microscopy also showed distinctive effects of pectin on DPPE and DPPC. We believe these data can be correlated with the action of this polysaccharide with biological lipidic surfaces with different polar heads, which may be relevant, generally speaking, to understanding the molecular mechanism of this bioactive compound for pharmaceutical purposes.

Influence of Potassium Ions on Act of Amphotericin B to the DPPC/Chol Mixed Monolayer at Different Surface Pressures

Amphotericin B (AmB) is an antifungal drug that rarely develops resistance. It has an affinity with the cholesterol on mammalian cell membranes, disrupting the structure and function of the membranes, which are also affected by potassium ions. However, the mechanism is unclear. In this paper, the Langmuir monolayer method was used to study the effects of potassium ions on the surface pressure–mean molecular area of isotherms, elastic modulus and the surface pressure–time curves of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/cholesterol (DPPC/Chol) monolayer and a DPPC/Chol/AmB monolayer. The morphology and thickness of the Langmuir–Blodgett films were studied via atomic force microscopy. The results showed that AmB can increase the mean molecular area of the DPPC/Chol mixed monolayer at low pressures (15 mN/m) but reduces it at high pressures (30 mN/m). The potassium ions may interfere with the effect of AmB in different ways. The potassium ions can enhance the influence of AmB on the stability of monolayer at low surface pressures, but weaken it at high surface pressures. The potassium ions showed significant interference with the interaction between AmB and the cholesterol-enriched region. The results are helpful for us to understand how the effect of amphotericin B on the phospholipid membrane is interfered with by potassium ions when amphotericin B enters mammalian cell membrane.